/usr/share/gocode/src/github.com/couchbase/moss/iterator.go is in golang-github-couchbase-moss-dev 0.0~git20170914.0.07c86e8-4.
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// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the
// License. You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an "AS
// IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
// express or implied. See the License for the specific language
// governing permissions and limitations under the License.
package moss
import (
"bytes"
"container/heap"
"io"
)
// DefaultNaiveSeekToMaxTries is the max number of attempts a forward
// iterator.SeekTo() will loop using simple Next()'s before giving up
// and starting a binary search for a given, forward seekToKey.
var DefaultNaiveSeekToMaxTries = 100
// An iterator tracks a min-heap "scan-line" of cursors through a
// segmentStack. Iterator implements the sort.Interface and
// heap.Interface on its cursors.
type iterator struct {
ss *segmentStack
cursors []*cursor // The len(cursors) <= len(ss.a) (+1 when lowerLevelIter).
startKeyInclusive []byte
endKeyExclusive []byte
prefixLen int
lowerLevelIter Iterator // May be nil.
closer io.Closer
iteratorOptions IteratorOptions
}
// A cursor rerpresents a logical entry position inside a segment in a
// segmentStack. An ssIndex < 0 and pos < 0 mean that the op/k/v came
// from the lowerLevelIter.
type cursor struct {
ssIndex int // Index into Iterator.ss.a.
sc SegmentCursor
op uint64
k []byte
v []byte
}
// StartIterator returns a new iterator on the given segmentStack.
//
// On success, the returned Iterator will be positioned so that
// Iterator.Current() will either provide the first entry in the
// iteration range or ErrIteratorDone.
//
// A startKeyInclusive of nil means the logical "bottom-most" possible
// key and an endKeyExclusive of nil means the logical "top-most"
// possible key.
//
// StartIterator can optionally include deletion operations in the
// enumeration via the IteratorOptions.IncludeDeletions flag.
//
// StartIterator can skip lower segments, via the
// IteratorOptions.MinSegmentLevel parameter. For example, to ignore
// the lowest, 0th segment, use MinSegmentLevel of 1.
func (ss *segmentStack) StartIterator(
startKeyInclusive, endKeyExclusive []byte,
iteratorOptions IteratorOptions) (Iterator, error) {
iter, err :=
ss.startIterator(startKeyInclusive, endKeyExclusive, iteratorOptions)
if err != nil {
return nil, err
}
return iter.optimize()
}
// startIterator() returns a new iterator on the given segmentStack.
//
// On success, the returned Iterator will be positioned so that
// Iterator.Current() will either provide the first entry in the
// iteration range or ErrIteratorDone.
//
// A startKeyInclusive of nil means the logical "bottom-most" possible
// key and an endKeyExclusive of nil means the logical "top-most"
// possible key.
//
// startIterator() can optionally include deletion operations in the
// enumeration via the IteratorOptions.IncludeDeletions flag.
//
// startIterator() can skip lower segments, via the
// IteratorOptions.MinSegmentLevel parameter. For example, to ignore
// the lowest, 0th segment, use MinSegmentLevel of 1.
func (ss *segmentStack) startIterator(
startKeyInclusive, endKeyExclusive []byte,
iteratorOptions IteratorOptions) (*iterator, error) {
if iteratorOptions.MaxSegmentHeight <= 0 {
iteratorOptions.MaxSegmentHeight = len(ss.a)
}
prefixLen := 0
if len(startKeyInclusive) > 0 &&
len(endKeyExclusive) > 0 {
prefixLen = sharedPrefixLen(startKeyInclusive, endKeyExclusive)
}
iter := &iterator{
ss: ss,
cursors: make([]*cursor, 0, len(ss.a)+1),
startKeyInclusive: startKeyInclusive,
endKeyExclusive: endKeyExclusive,
prefixLen: prefixLen,
iteratorOptions: iteratorOptions,
}
// ----------------------------------------------
// Add cursors for our allowed segments.
minSegmentLevel := iteratorOptions.MinSegmentLevel
maxSegmentLevel := iteratorOptions.MaxSegmentHeight - 1
ss.ensureSorted(minSegmentLevel, maxSegmentLevel)
for ssIndex := minSegmentLevel; ssIndex <= maxSegmentLevel; ssIndex++ {
b := ss.a[ssIndex]
sc, err := b.Cursor(startKeyInclusive, endKeyExclusive)
if err != nil {
return nil, err
}
op, k, v := sc.Current()
if op == 0 && k == nil && v == nil {
continue
}
iter.cursors = append(iter.cursors, &cursor{
ssIndex: ssIndex,
sc: sc,
op: op,
k: k,
v: v,
})
}
// ----------------------------------------------
// Add cursor for the lower level, if wanted.
if !iteratorOptions.SkipLowerLevel &&
ss.lowerLevelSnapshot != nil {
llss := ss.lowerLevelSnapshot.addRef()
if llss != nil {
lowerLevelIter, err := llss.StartIterator(
startKeyInclusive, endKeyExclusive, IteratorOptions{})
llss.decRef()
if err != nil {
return nil, err
}
if lowerLevelIter != nil {
k, v, err := lowerLevelIter.Current()
if err != nil && err != ErrIteratorDone {
return nil, err
}
if err == ErrIteratorDone {
lowerLevelIter.Close()
}
if err == nil {
iter.cursors = append(iter.cursors, &cursor{
ssIndex: -1,
op: OperationSet,
k: k,
v: v,
})
iter.lowerLevelIter = lowerLevelIter
}
}
}
}
// ----------------------------------------------
// Heap-ify the cursors.
heap.Init(iter)
if !iteratorOptions.IncludeDeletions {
entryEx, _, _, _ := iter.CurrentEx()
if entryEx.Operation == OperationDel {
iter.Next()
}
}
return iter, nil
}
// Close must be invoked to release resources.
func (iter *iterator) Close() error {
if iter.lowerLevelIter != nil {
iter.lowerLevelIter.Close()
iter.lowerLevelIter = nil
}
if iter.closer != nil {
iter.closer.Close()
iter.closer = nil
}
return nil
}
func (iter *iterator) InitCloser(closer io.Closer) error {
if iter.closer != nil {
return ErrAlreadyInitialized
}
iter.closer = closer
return nil
}
// Next returns ErrIteratorDone if the iterator is done.
func (iter *iterator) Next() error {
if len(iter.cursors) <= 0 {
return ErrIteratorDone
}
lastK := iter.cursors[0].k
for len(iter.cursors) > 0 {
next := iter.cursors[0]
if next.ssIndex < 0 && next.sc == nil {
err := iter.lowerLevelIter.Next()
if err == nil {
next.k, next.v, err = iter.lowerLevelIter.Current()
if err == nil && len(iter.cursors) > 1 {
heap.Fix(iter, 0)
}
}
if err != nil {
iter.lowerLevelIter.Close()
iter.lowerLevelIter = nil
heap.Pop(iter)
}
} else {
err := next.sc.Next()
if err != nil {
if err != ErrIteratorDone {
return err
}
heap.Pop(iter)
} else {
next.op, next.k, next.v = next.sc.Current()
if next.op == 0 {
heap.Pop(iter)
} else if len(iter.cursors) > 1 {
heap.Fix(iter, 0)
}
}
}
if len(iter.cursors) <= 0 {
return ErrIteratorDone
}
if !iteratorBytesEqual(iter.cursors[0].k, lastK) {
if !iter.iteratorOptions.IncludeDeletions &&
iter.cursors[0].op == OperationDel {
lastK = iter.cursors[0].k
continue
}
return nil
}
}
return ErrIteratorDone
}
func iteratorBytesEqual(a, b []byte) bool {
i := len(a)
if i != len(b) {
return false
}
for i > 0 { // Optimization to compare right-hand-side of keys first.
i--
if a[i] != b[i] {
return false
}
}
return true
}
func (iter *iterator) SeekTo(seekToKey []byte) error {
key, _, err := iter.Current()
if err != nil && err != ErrIteratorDone {
return err
}
if key != nil {
cmp := bytes.Compare(seekToKey, key)
if cmp == 0 {
return nil
}
if cmp > 0 {
// Try a loop of naive Next()'s for several attempts.
err = naiveSeekTo(iter, seekToKey, DefaultNaiveSeekToMaxTries)
if err != ErrMaxTries {
return err
}
}
}
// The seekToKey is before our current position, or we gave up on
// the naiveSeekTo(), so start a brand new iterator to replace our
// current iterator, bounded by the startKeyInclusive.
//
if bytes.Compare(seekToKey, iter.startKeyInclusive) < 0 {
seekToKey = iter.startKeyInclusive
}
iterNew, err := iter.ss.startIterator(seekToKey,
iter.endKeyExclusive, iter.iteratorOptions)
if err != nil {
return err
}
iterOld := *iter // Clone current iterator before overwriting it.
iterOld.closer = nil
iter.cursors = iterNew.cursors
iter.lowerLevelIter = iterNew.lowerLevelIter
iterOld.Close()
_, _, err = iter.Current()
return err
}
func naiveSeekTo(iter Iterator, seekToKey []byte, maxTries int) error {
for i := 0; maxTries <= 0 || i < maxTries; i++ {
key, _, err := iter.Current()
if err != nil {
return err
}
if bytes.Compare(seekToKey, key) <= 0 {
return nil
}
err = iter.Next()
if err != nil {
return err
}
}
return ErrMaxTries
}
// Current returns ErrIteratorDone if the iterator is done.
// Otherwise, Current() returns the current key and val, which should
// be treated as immutable or read-only. The key and val bytes will
// remain available until the next call to Next() or Close().
func (iter *iterator) Current() ([]byte, []byte, error) {
entryEx, key, val, err := iter.CurrentEx()
if err != nil {
return nil, nil, err
}
op := entryEx.Operation
if op == OperationDel {
return nil, nil, nil
}
if op == OperationMerge {
var valMerged []byte
valMerged, err = iter.ss.getMerged(key, val, iter.cursors[0].ssIndex-1,
iter.iteratorOptions.base, ReadOptions{})
if err != nil {
return nil, nil, err
}
return key, valMerged, nil
}
return key, val, err
}
// CurrentEx is a more advanced form of Current() that returns more
// metadata. It is used when IteratorOptions.IncludeDeletions is
// true. It returns ErrIteratorDone if the iterator is done.
// Otherwise, the current operation, key, val are returned.
func (iter *iterator) CurrentEx() (
entryEx EntryEx, key, val []byte, err error) {
if len(iter.cursors) <= 0 {
return EntryEx{}, nil, nil, ErrIteratorDone
}
cursor := iter.cursors[0]
return EntryEx{Operation: cursor.op}, cursor.k, cursor.v, nil
}
func (iter *iterator) Len() int {
return len(iter.cursors)
}
func (iter *iterator) Less(i, j int) bool {
a := iter.cursors[i].k[iter.prefixLen:]
b := iter.cursors[j].k[iter.prefixLen:]
c := bytes.Compare(a, b)
if c < 0 {
return true
}
if c > 0 {
return false
}
return iter.cursors[i].ssIndex > iter.cursors[j].ssIndex
}
func (iter *iterator) Swap(i, j int) {
iter.cursors[i], iter.cursors[j] = iter.cursors[j], iter.cursors[i]
}
func (iter *iterator) Push(x interface{}) {
// Push and Pop use pointer receivers because they modify the slice's length,
// not just its contents.
iter.cursors = append(iter.cursors, x.(*cursor))
}
func (iter *iterator) Pop() interface{} {
n := len(iter.cursors)
x := iter.cursors[n-1]
iter.cursors = iter.cursors[0 : n-1]
return x
}
// --------------------------------------------
// The optimize method tries to optimize an iterator. For example,
// when there's only a single segment, then the heap can be avoided by
// using a simpler, faster iteratorSingle implementation.
func (iter *iterator) optimize() (Iterator, error) {
if len(iter.cursors) != 1 {
return iter, nil
}
cur := iter.cursors[0]
if cur.ssIndex == -1 && cur.sc == nil {
// Optimization to return lowerLevelIter directly.
return iter.lowerLevelIter, nil
}
seg, ok := iter.ss.a[cur.ssIndex].(*segment)
if !ok || seg == nil {
return iter, nil
}
return &iteratorSingle{
s: seg,
sc: cur.sc,
op: cur.op,
k: cur.k,
v: cur.v,
closer: iter.closer,
options: iter.ss.options,
iteratorOptions: iter.iteratorOptions,
}, nil
}
// --------------------------------------------
// sharedPrefixLen returns the length of the prefix shared by a and b,
// which can might be 0 length.
func sharedPrefixLen(a, b []byte) int {
i := 0
for i < len(a) && i < len(b) {
if a[i] != b[i] {
return i
}
i++
}
return i
}
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